The present invention relates to an apparatus and method for the electrical stimulation of muscle which rely upon a particular pattern of electrical stimulation.
It is well known that muscle contraction is caused by neural stimulation. Contraction occurs when an action potential is conducted down a nerve to a neuromuscular junction, the signal is then communicated to muscle cells and leads to the stimulation of the release of calcium ions into the cytoplasm of muscle cells which thereby modifies interactions between contractile proteins resulting in muscular contraction.
It has been long established that the application of an electrical field to muscles results in an artificially induced contraction of said muscles. Furthermore, as well as directly causing muscular contraction, electrical stimulation at specific frequencies can also modify the phenotype of a muscle. For instance, prolonged stimulation of a fast-twitch muscle with a uniform frequency of 10 Hz results in the fast-twitch muscle developing slow-twitch characteristics, namely increased endurance, but with less power than would be normal for fast-twitch muscle. Conversely, prolonged stimulation of a slow-twitch muscle with an intermittent frequency of 30-50 Hz results in the slow-twitch muscle developing fast-twitch characteristics, namely increased power, but with less endurance than would be normal for slow-twitch muscle.
It has been suggested that electrical stimulation of muscles may be a useful means of improving strength and/or endurance of incapacitated muscle (due to injury, under-use or some pathological condition). For a number of years muscles have been stimulated by Faradic stimulation delivering uniform frequencies (of around 30-50 Hz) with the aim of beneficially affecting the muscle. However, these treatments have at best been ineffective and at the worst harmful to the muscle in the long term.
UK Patent GB 2 156 682 examined the electrical discharge of nerves innervating muscle with an aim of developing a means of beneficially stimulating muscle. It discloses a method of recording electrical discharges from nerves innervating muscles. A signal generated on the basis of the recording is then used to "electrotrophically" stimulate muscle. Electrotrophic stimulation is defined as "the electrical stimulation of muscle fibre using a stimulating signal containing information effective to cause structural and/or functional change of muscle fibre without requiring the muscle fibre to respond mechanically to the stimulation". However the stimulating signal of GB 2 156 682 is complex and difficult to generate.